Shower pan base

We are getting new home build. The builder recessed the shower pan area when they pour concrete. We are not suppose to get recess tile pan. We want fiberglass. What material should they use to refill? Since they didn't pour concrete while they were doing foundation, is there gone be any problem later?

How much is it recessed? Fiberglass is less expensive than a tiled shower and can last a long time, but a properly installed tiled shower can be a lifetime install - a fiberglass one won't be. Depends somewhat on how much fill is needed, but there shouldn't be a problem filling it in. In fact, you could build a wooden platform to bring it level, so you could do the recessed, tiled, shower later without cracking out whatever is installed to fill it in now.

The only reason I'd use fiberglass verses a tiled shower is if cost was a big issue. The key here is a 'properly' installed shower, if done right, it should be problem free until you decide to remodel.

There are many fiber glass shower pans out that have somewhere between a 3/4"-5" lip to them. You might select one, align the waste pipe and infill the hole with more cement so that your new shower has a drop down shower?

It is quit common for builders to prepare for a "Drop Down" shower in the South.